Melt spinning process and apparatus



June 30, 1970 E sw so ETAL 3,511,412

MELT SPINNING PROCESS AND APPARATUS Original Filed Jan. 19. 1965 EUGENE A.SW WILLIAM H. HARL GRADY N.DU

ATTORNEY United States Patent 3,517,412 MELT SPINNING PROCESS AND APPARATUS Eugene A. Swanson, Disputanta, and William H. Har lacher and Grady N. Dulin, Jr., Chester, Va., assignors to Allied Chemical Corporation, New York, N.Y., a corporation of New York Original application Jan. 19, 1965, Ser. No. 426,631. Divided and this application June 18, 1968, Ser. No. 752,414

Int. Cl. D01d 13/02 US. Cl. 1t-8 1 Claim ABSTRACT OF THE DISCLOSURE Melt spinning apparatus having a heated sleeve sealed around the spinneret, open at its lower end to a spinning tower wherein there is a gas outlet and a gas inlet therebelow, and wherein preferably the major portion of the entering air flows down the tower and a minor portion flows up the tower.

This is a division of application Ser. No. 426,631 filed Jan. 19, 1965, now abandoned.

This invention relates to the melt spinning of e-polycaproamide compositions.

The invention is particularly useful for spinning polycaproamide at high speeds and for spinning polycaproamide of very high molecular weight and high melt viscosity into filaments for production of high strength yarns for use, e.g., in automobile tire. cords.

Yarns of polycaproamide, otherwise known as nylon 6, find widespread use in applications which can benefit from the high strength, suppleness, uniformity and dura bility of said yarns. Typical applications include high strength webbing such as safety belts; protective coverings such as tarpaulins; netting; and reinforced structures such as tires, conveyor belt and power transmission belts. In these industrial applications of synthetic yarns, improvements in strength are continually sought since such improvements increase the effectiveness of the yarn in a par ticular utilization, or permit the use of less yarn without sacrifice of strength of the overall structure. Hereover for these high strength yarns and for other synthetic filaments, a high rate of filament production, which must start with a high rate of spinning, is very important economically.

This invention provides a process allowing the melt spinning of higher molecular weight polycaproamide than could be spun using the methods heretofore generally known, and allowing the spinning of polycaproamide filaments at higher rates than usually obtainable for a given polymer molecular weight.

The process of the present invention comprises extruding into a spinning chamber an e-polycaproamide melt which is at a temperature of about 250 C.-300 C. to form continuous filament therefrom downwardly through a spinneret and into a zone of the chamber immediately therebelow wherein the resulting filaments contact hot quiescent gas. At a point /2 inch downward from the spinneret, the temperature measured by a ther mocouple is at least 40 C. higher than the temperature of the polycaproamide melt which is being extruded, and is at least 315 C.; but is not above the temperature, of

the order of 400- C., where polymer degradation sets in under spinning conditions. Contact of the filaments with hot quiescent gas in a zone at temperatures of at least 315 C. is maintained, as the filaments descend through the spinning chamber, for a limited time of not over /2 second. Then the filaments pass into contact with cooler gas in a zone having temperature below the temperature of the extruded melt; and then into contact with still cooler gas in a zone having temperature at least 30 C. below the melting point of the polycaproamide, whereby the filaments are cooled and solidified. It will be recognized that the above cited temperatures are those measured by a thermocouple and may be due to absorbed radiant heat as well as to heat absorbed by heat exchange with the hot quiescent gas.

Contact of the filaments immediately below the spinneret with quiescent gas in a zone having the elevated temperatures used in our process, viz. at least 40 C. higher than the temperature of the melt being extruded, we have found, facilitates spinning of polymers which would be too viscous to pass through the spinneret holes and form good quality uniform filaments, or would not allow spinning at the same high rate, when using normal spinning conditions wherein the temperature in the spinning chamber at and just below the spinneret is about the temperature of the molten extrudate, or cooler.

It is a surprising fact that in our process, temperatures immediately below the spinneret are maintained well above those which can safely be maintained in the molten extrudate itself without degrading it. While we do not intend to be bound by theories, we believe the successful use of temperatures of 315 C. and above in our process is connected with use of quiescent gas, and with volatilization from the polycaproamide filaments of low molecular weight constituents, especially lactam monomer, while the filaments contact this gas. The evolution of the monomer may create a protective influence on the filament against the effects of hot gas, and at the same time improve the spinnability of the melt, e.g., by providing a lubricating effect at the surface of the filaments being extruded.

A preferred temperature range /2 inch down from the spinneret is about 320 C.-380 C.; and the temperature should of course be no higher than that where polymer degradation sets in, viz. about 400 C. It will be appreciated that the extent of polymer degradation is a function of time of exposure to the hot gas as well as temperature, and that at relatively short exposure times the higher temperatures can be used.

Preferably the filaments, after their contact with the hot quiescent gas and during their cooling, are passed in not over 2" of their travel from a zone at temperature equal to the melting point of the polycaproamide (about 210-220 C.) into a zone at temperature some 30 C. below the melting point of the polycaproamide. Thereby the filaments are cooled rapidly from a temperature above the melting point of the polycaproamide to a temperature well below the melting point, with a beneficial effect on crystallinity and related properties.

That portion of the gas in the zones which are cooler than the molten extrudate can be in any state of motion which is nonturbulent; e.g., part of this gas can be quiescent like the hot gas, and another part can be in smooth flow cocnrrent, countercurrent, or across the filaments as generally known for quench gas flow in melt spinning processes. There will always be some gas moving out of the quiescent zone, which gas should be drawn out of the spinning chamber, to remove from the spinning chamber the volatilized lactam in this gas. Preferably this gas will be Withdrawn in the upper section of the chamber, e.g., just below the quiescent Zone, and will be taken out through a heated pipe or the like, to avoid condensation of its lactam content in the spinning chamber or on the filaments when being cooled.

Specific embodiments illustrative of the invention and of the best mode contemplated by us of carrying it out are described below with reference to the accompanying drawing, and in the examples which follow. The drawing schematically illustrates a sectional elevation taken along the vertical axis of the spinning chamber of a spinning apparatus suitable for carrying out the process of this invention.

In the illustrated embodiment of the invention, a spinning tower is divided into an upper section 20, a midsection 22, and a lower section 24. The tower provides a spinning chamber the upper part of which is defined by a horizontal spinneret 14 having a multiplicity of orifices 16, and by vertical cylindrical shield 12 comprising sections 38 and 40 described below. The upper section, 20, of the tower comprises said spinneret and shield, and outer wall sections 28 and 60 forming around shield 12 an outer chamber 30. Chamber 30 is provided with exhaust ports or outlets 32 which lead to a vacuum pump or other suitable means, not shown, for withdrawing gas. These outlets 32 are jacketed for heating to prevent condensation of lactam therein. Outer wall section 28 terminates below in an inwardly projecting lip 34, forming a bottom for outer chamber 30. Outer wall section 60 is removably connected, e.g., by a liquid seal 62 or deformable gasket or packing, with wall section 28 and is terminated above by connection to spinneret 14, thus allowing ready disassembly of the tower for maintenance of the spinneret.

Shield 12 comprises upper section 38 and adjustable lower section 40. Heating means are provided upon the upper section 38 for heating the uppermost region of spinning chamber 10, such means including suitably a band electric heater 44. The upper and lower sections 38 and 40 of the heated shield are constructed of a heat conducting rust resistant alloy, preferably stainless steel. The upper section is in tight physical contact with the lower section to transfer heat from the heated upper portion to the nonheated lower portion, thereby providing a thermal gradient from the end of the electric band heater 44 to the bottom of the lower section 40. This upper section preferably closely surrounds the area immediately below the outermost spinneret orifices, being at a radial distance from those outermost orifices suitably about A inch-2 inches.

The lower section 40 of the heated shield is vertically adjustable by means of set screw 46 so that the vertical distance from the face of the spinneret 14 to the lower edge, 48, of section 40 may be adjusted as desired. The preferred adjustment is about 3 inches to about 8 inches.

We have found that the heated shield must be sealed around the spinneret face to prevent air currents at the spinneret face sufficient to cause filament flicking at the spinneret opening which will depreciate the physical properties and increase variations in filament diameter. To this end, the upper surface of section 38 of the heated shield is provided with a packing retainer 50 for receiving a circular gasket or packing 52 such as an O-ring; or other sealing means, constructed to withstand temperatures in excess of 400 C. can be used, e.g., a liquid seal.

Means are provided for urging the packing 52 into engagement with the face of the spinneret, comprising a series of pistons 54 attached to section 38 and received in cylinders 56, which cylinders contain compression 4 springs 58. Springs 58 bear against lip 34 to urge pistons 54 and wall section 38 upward.

Below lip 34, lower wall section 42 extends downward forming the midsection 22 of the spinning chamber 10, down to gas inlets 26. Below inlets 26 walls 42 continue downward to form the lower section 24 of spinning chamber 10. The total length of the spinning chamber will usually be about 10 feet in the apparatus of the drawing.

In operation the heating element 44 is turned on and allowed to reach thermal equilibrium. The lower section 40 of the heated sleeve or shield is adjusted with the set screw 46 to the desired vertical distance from the spinneret face to the lower edge 48 of the shield. Molten polymer is pumped into the spinneret 14 from which it passes through the orifices 16 and drops as filaments in the spinning chamber 10. With the tower in raised position, the top of shield 12 is sealed against spinneret 14, thus separating the upper zone 20 of spinning chamber 10 from the outer surrounding chamber 30.

In the particular spinning tower illustrated, relatively cool gas, suitably air, enters the spinning chamber 10 through inlets 26. A minor portion of the air moves upwardly through midsection 22 toward the heated shield 13 while the remainder of the air moves downwardly through lower section 24 in the direction of travel of the filaments 18. The air flow through inlet 26 is maintained at a rate suitably in the range of about 20 standard cubic feet per minute to about 160 standard cubic feet per minute for a 9-inch diameter tower. One advantage provided by use of our heated shield and hot quiescent gas zone within the shield is that gas fiow rates into the the spinning chamber prove less critical than where such heated shield is not used.

Between about 5 percent and about 20 percent of the total volume of entering gas passes upwardly through the midsection 29 of the spinning chamber. Gas from this section 22 and from within shield 12 is drawn through the space between the bottom of the heated shield and the annular lip 34, into the outer chamber 30 and thence out the outlets 32. These outlets are kept at temperatures of the order of about 300 to about 400 C. to avoid condensation of organic vapors therein, e.g., lactam. The outlets are suitably at a level from just below the spinneret to about a foot below the lower edge 48 of the heated shield, a preferred location being within about 3 inches above or below the lowest setting of the lower edge 48 of shield 12.

The gas entering through inlets 26 can be maintained at any desired temperature which will generally be at least 30 C. below the polycaproamide melting point so as to effect the desired quick cooling of the filaments when their temperature is near the melting point. The entering gas may be made to enter the chamber at uniform flow into the chamber throughout the entire periphery of the chamber, or the flow through inlets 25 can be adjusted so as to be unequal going around the periphery. In fact the gas can enter from only one inlet, with a gas outlet provided opposite thereto, to produce cross-flow quenching. Gas distributing means such as grids, screens, cloths and the. like will advantageously cover inlets 26 to control the gas flow pattern.

The humidity of the entering gas can be established at any given desired humidity level, a suitable humidity range being from about 40 percent to about percent relative humidity at 28 C. A low moisture content of the entering gas, corresponding to vapor pressure of say about 10-100 mm. of mercury, may contribute to good properties in the final filaments.

A cooling temperature curve for the gas in the Spinning chamber, plotted against the distance from the spinneret face, is indicative of the mechanical and process parameters of the spinning system. A typical cooling curve, characteristic of spinning when employing quiescent gas in the region near the spinneret but not heating this region above the temperature of the extruded melt, is

provided by the system disclosed in copending US. application Ser. No. 262,546 of G. N. Dulin, Jr., filed Mar. 4 1963, said curve being approximated by the following formula for the spinning of polycaproamide at about 260 C. melt temperature.

where T===the temperature in centigrade degrees of the gas at D distance (in inches) from the spinneret face.

By comparison, in the above outlined embodiment of the present invention for spinning at melt temperature of about 260 C. a typical cooling curve in the quiescent region is approximated by the formula:

T and D having the same meaning as above.

This cooling curve is a power function wherein the change in T is very small for the first two inches, but the change in T increases at accelerated rates from 2 to 5 inches, and increases with considerable acceleration at distances approaching the overall length of the heated shield, namely 5 to 8 inches. This cooling curve is essentially the opposite of a normal nylon -6 cooling curve such as that described above, characteristic of melt extrusion performed without our heated shield.

The following Table I further illustrates the distinction between prior art processes and the process according to this invention with respect to the gas temperature drop in a nylon 6 system.

It has been found that utilizing the process of the present invention, yarns can be produced showing improvement in ultimate tensile strength of about 0.5 gram per denier and more, versus yarns spun in chambers operating at conventional temperatures; and this gain is without sacrifice of the other important physical properties of the yarn. Such improvement is of significant importance in the applications of high strength yarn. Moreover yarn spun in accordance with this invention shows improved performance upon drawing and windup over yarn spun using conventional temperatures in the spinning chamber. The improvements are especially evident for yarn spun from high molecular weight polycaproamide, having molecular weight of at least about 24,000 number average, in particular such polycaproamide of molecular weight at least 25,000 and analyzing not over milliequivalents of primary amino groups per kilogram of polymer and the balance of the end groups being substantially all carboxyls, as disclosed and claimed in copending application of Ian C. Twilley, Ser. No. 426,632, filed Jan. 19, 1965, now Pat. No. 3,386,967.

The polycaproamide melt which is spun by the process of this invention can contain various dissolved or finely dispersed additives such as stabilizing agents, delustrants, pigments, blended-in polymers, latent cross-linking agents, adhesion-promoting agents, antistatic agents, etc.

The same principles are applicable in the melt spinning of other thermoplastic polymers generally, to greater or lesser degree depending upon the extent to which they tend to build up volatile impurities during spinning, in particular impurities that deposit on the spinneret. Such impurities include straight chain and cyclic low molecular weight oligomers and cyclic monomers from polyhexamethylene adipamide, polyenantamide, polyoctanamide, polynonanamide, polydecanamide, polyundecanamide, polydodecanamide, polyethylene terephthalate, polyethylene isophthalate and polyethylene 2,6 and 2,7 naphthalene dicar-boxylate.

Several embodiments of this invention are illustrated by the following examples. Unless otherwise stated, the quantities employed in all examples are expressed as percent by weight. The ultimate tensile strength and ultimate elongation, number average molecular weights and toughness index are defined as follows:

Definitions Number average molecular weight is defined as M,,=NiMi/Ni where Ni are the number of molecules of molecular Weight Mi.

The number average molecular weight is determined from the equation:

(NHz-l-COOH) where (NH )==milliequivalents of amine per kilogram of washed and dried polymer and,

(COOH)=milliequivalents of carboxyl per kilogram of washed and dried polymer.

Amine and carboxyl groups are determined by direct titration in a suitable solvent.

Ultimate tensile strength All ultimate tensile strengths are measured on a Scott Tensilgraph lP-4 using Spruan'ce air-operated cord clamps and a gage length of 10 inches. A weight of 10 kilograms was used over carriage weight of 2 kilograms. Four breaks on each sample are taken, or more, so that four breaks fall within /2 inch on the load (vertical) scale. Reading vertically, record the breaks and calculate the average.

Ultimate elongation Toughness index is measured by the area under the stress-strain curve from the origin out to the breakpoint. It is a measure of the amount of work required to rupture the fiber and is an indication of relative durability under mechanical fatigue.

For tire yarns, a simplified relationship is used as an approximation for toughness index. This is ultimate tensile strength (UTS) in grams per denierx square root of the ultimate elongation (UE) in percent. This (UTS) (UE) value is used in the following examples.

The examples which follow describe completely specific embodiments illustrative of our invention and of the best mode contemplated by us of carrying out our invention; but the invention is not to be interpreted as limited to all details of the examples.

EXAMPLE 1 This example utilized polycaproamide of number average molecular weight 30,800 and relatively low melt viscosity prepared using sebacic acid to combine with amine groups as described in the copending US application of Ian C. Twilley, Ser. No. 426,632 filed Jan. 19, 1965, Example 1 thereof. The polymer contained, as heat stabilizing agents, a trace amount of dissolved copper compound and a small amount of a ketone/diarylamine con- 7 densation product as in Schule U.S.P. 3,003,995 of Oct. 10, 1961.

A spinning apparatus as illustrated in the accompanying drawing and as hereinabove described Was provided with an annular shield heated with a 1,000-watt electric band heater around its upper surface, the shield being sealed by gaskets against the spinneret. Each hole of the 136-hole spinneret was of 0.013 inch diameter. The shield was adiusted to total length of 6.01 inches. Its internal diameter was 9.25 inches. The length of the quiescent region thus created in this spinning apparatus was six inches; the length of the countercurrent flow region was seven feet; and the length of the cocurrent region was ten feet. The inner diameter of the tower was about 9 inches, which was about inch greater than the diameter of the outermost ring of orifices in the spinneret.

Air at 28 C. and relative humidity, at 28 C., of 65% was admitted through inlet means 26 at a rate of 63 cubic feet per minute. Six cubic feet per minute of gas was re moved through exhaust ports 32. The cooled extrudate was wound up as undrawn multifilament yarn at a rate of 1500 feet per minute. The undrawn yarn was subsequently drawn to a draw ratio of about 4.9 employing conventional drawing and yarn heating means.

Tire yarn produced using the annular heated shield of this invention was compared with tire yarn produced from the same apparatus but without the shield. Table II below summarizes the results obtained, and shows significant improvement in yarn strength and toughness and in performance upon drawing and winding when using the process of this invention, in which a heated annular shield is employed, versus operation without the heated shield.

EXAMPLE 2 Table III shows the results of spinning a sebacic acid terminated polymer with a lower number average molecular weight than that used in Example 1, and with the procedure and conditions of Example 1 except that the length of the heated annular shield used was 5 inches. Data tabulated in Table III represents an average of 6 spinning trials with 5 different polycaproamide polymers. It will be appreciated that in Table III, as in Table II, higher strength, tougher yarn was produced and better performance in drawing was obtained when using the heated shield than without it.

EXAMPLE 3 A polycaproamide spinning polymer, having a normal number average molecular weight for spinning, viz about 20,000 molecular weight, and a normal melt viscosity for its molecular weight was used in this example. The polymer was spun using the process and apparatus described in Example 1, and shown in the drawing of this application. The length of the heated annular shield was 610 inches.

The results obtained are summarized in Table IV. There is improvement by using the heated annular shield particularly in toughness and in drawing performance, but it is notable that the improvement is less marked with this polymer than with the polymer of Example 1.

TABLE II With Control heated without annular annular shield shield Number average molecular weight 30, 800 30, 800 Temperature, molten polymer as it enters the spinneret, C 260 260 Type yarn, denier/number filaments 840/136 840/136 Quench gas temperature, from spinneret 333 224 Quench gas temperature, 3 from spinneret face,

317 162 Quench gas temperature, 6" from spinneret face,

230 125 Ultimate elongation, percent 18. 1 17. 8 Ultimate tensile strength, grams/de 10. 11 9. 85 Toughness index, UTSX UE 43. 0 41. 55 Yarn, breaks per pound 0 014 Yarn, wraps per pound 0 .043

TABLE III Average polymer number average molecular weight 23, 050 23, 030 Temperature of molten polymer as it enters the spinneret, C 260 260 Type yarn, denier/filament 840/136 840/136 Quench gas temperature, from spinneret face, 335 223 322 161 15. 9 15. 88 9. 9. 80 Toughness index UISXUE 30. 7 38. 65 027 005 Yarn wraps per pound 15 12 TABLE IV With Control heated without annular heated shield shield Temperature of the molten polymer as it enters the spinneret, C 26 261 Tire yarn, denier/number filaments.... 840/136 840/136 Quench air temperature, from the sp neret face, C 336 223 Quench air temperature, 3 from the spinneret ce, C 307 Ultimate elongation, percent 16. 0 15. 7 Ultimate tensile strength, grams/denier 9. 20 9. 10 Toughness index, UTSXUE I 36. 8 36. 0 Yarn, breaks per pound 037 062 Yarn, wraps per pound 047 0 EXAMPLE 4 A series of polycaproamide polymers were spun at progressively higher molecular weights and molten polymer temperatures. The apparatus and procedure including the heated annular shield were essentially the same as described in Example 1 and illustrated in FIG. 1 of this application, the length of the heated shield being set at 6 inches, and a 1000-watt electric band heater 1 /2 inches in width was used.

Table V summarizes the results of tests conducted with and without a heated shield.

In Series (A) of the tests summarized in Table V, the polycaproamides used were prepared by a conventional procedure and had normal melt viscosity for their number average molecular weights. In series (B), the polycaproamide polymers were prepared using sebacic acid termination as described in the copending U.S. application of Ian C. Twilley, Ser. No. 426,632, filed Jan. 19, 1965, which describes the production of polycaproamide characterized by low melt viscosity for the number average molecular weight, permitting spinning at higher than normal number average molecular weights.

It will be appreciated that use of our process as in this example allowed the spinning of polymers which were unspinnable under conventional temperature conditions in the spinning chamber because of their high melt viscosity; and with spinnable polymers, gave improved properties versus conventional spinning conditions. Especially strong, tough filaments were obtained in the tests of this example upon spinning polycaproamide of number average molecular weight at least about 24,000. In particular this was true using the very high number average molecular weight (30,000 and above) polycaproamide having primary amino group analysis not over 10 milliequivalents per kilogram and the balance of the end groups substantially all carboxyl, used in part B of this example.

TABLE V(A) Polymer Series (A) number, Grams per Relative with heated average denier, Toughness formic Molten polymer annular molecular ultimate index, acid, temperature, C. shield weight tenacity UTSXUE viscosity Comments 20, 700 9. 20 36. 8 57. Spinning and drawing performance, OK. 20, 700 9.10 36.0 57. 0 Do. 22, 300 9. 42 37. 7 77. Do. 22, 300 9.10 36.0 77.5 Poor drawing, and too high a spinning pack pressure develops. 23, 450 9. 54 38. 3 94.0 Spinning and drawing performance, OK. 23, 450 9.00 35. 65 94. 0 Poor spinning and drawing performance. 24. 000 9. 60 38. 4 100. 0 Spinning and drawing performancesatisfactory. 24,000 100. 0 Could not spin, pack pressure too high. 24, 600 9. 66 38. 6 112.0 Some polymer degradation. 24, 600 Could not spin.

TABLE V(B) Grams per Series (B) with Polymer number, denier, Toughness Molten polymer heated annular average molecular ultimate index, temperature, C. shield Weight tenacity UISXUE Comments 30, 550 10.17 43. 2 Spinning and drawing satisfactory. 30, 555 9. 87 41. 2 Do. 31, 880 10.29 43. 7 Do. 31, 830 9. 80 40. 8 Spinning and drawing perfonnance poor. 33, 000 10. 44. 15 Spinning and drawing satisfactory. 33, 000 9. 70 40. 4 Poor yarn quality, snort spin pack life. 33, 580 10. 42 44. 34 Spun and drew satisfactorily. 33, 580 Yarn could only be spun with difficulty. 34, 200 10. 44. 4 Some loss in color of yarn. 34,200 Could not spin, too high pressures at spinneret outlet holes.

When polycaproamide containing blended-in polyethylene terephthalate fiber-forming polymer is spun using procedure and conditions as in this Example 4, improvements are realized in yarn properties, especially strength and toughness, similar to those shown in the tests of Example 4, Series B above.

Although particular embodiments of the invention are herein disclosed for purposes of explanation and il1ustration, modifications thereof will be apparent to those skilled in the art to which the invention pertains. Reference should accordingly be had to the appended claims in determining the scope of the invention.

We claim:

1. A spinning tower comprising a horizontal spinneret with at least one vertical orifice therein; sealed around said spinneret and closely surrounding the area immediately below the outermost orifices thereof, a downwardly extending shield open at its lower end and provided, at least at its upper end, with heating means; a chamber outside said shield and in communication with the exterior References Cited UNITED STATES PATENTS 2,335,122 12/ 1943 Dreyfus. 3,053,611 9/1962 Griehl. 3,299,469 1/1967 Charlton.

FOREIGN PATENTS 852,351 10/1960 Great Britain.

WIL'BUR L. MCBAY, Primary Examiner 

